In discrimination training with the Lyons' blackout method, pecks to the negative stimulus are prevented by darkening the chamber each time the subject approaches the negative stimulus. Stimulus generalization along a stimulus dimension was measured after training with this method. For comparison, generalization was also measured after reinforced responding to the positive stimulus without discrimination training, and after discrimination training by extinction of pecks to the negative stimulus. The blackout procedure and the extinction of pecks to the negative stimulus both produced a peak shift in the generalization gradients. The results suggest that after discrimination training in which the positive and negative stimulus are on the same continuum, the blackout method produces extinction‐like effects on generalization test